Champion Novak Djokovic was unable to draw much support from the crowd at Rod Laver Arena during his 6-1, 6-2, 3-6, 6-3 semi-final win over sentimental favourite Roger Federer on Thursday, but the Serb found vital friends in the weather and the net-cord.

Two sets of the best tennis of his career against Federer sent the world number one hurtling toward a sixth final at Melbourne Park.

But it left most in the 15,000-seat stadium cold.

Instead, there was a standing ovation for Federer when he returned to the court for the third set and proceeded to knuckle down to turn the match into a contest.

Most in the stands were delighted when Federer finally broke Djokovic's serve in an epic sixth game.

Were the stadium's retractable roof not already open, it might have blasted off with the noise generated by Federer serving out the set.

Yet, as swiftly as the Swiss seized the momentum it was stolen from him by a change in the weather that forced the roof to close.

Djokovic used the few minutes break in play to marshall his forces and wait for an opportunity.

It ultimately arrived in a dramatic eighth game that featured one of the most exquisite points of the tournament.

At 15-30 and under pressure on serve, Federer rushed to the net to prod a drop-shot into the corner which Djokovic retrieved with a brilliant lob.

The Swiss pumped his 34-year-old legs back to the baseline to return the lob and darted cross-court to parry back a Djokovic smash.

Federer had no business returning the Serb's second cross-court volley but scrambled to swing for a desperate backhand and the passing shot burned the line.

The crowd erupted in another standing ovation as Federer pumped his fists in celebration.

"His defence was terrific that point," Djokovic, who will bid for a sixth title against either Andy Murray or Milos Raonic, told reporters.

"After it was done, I had to just forget about it and focus on the next point."

Net-cord sets up vital break for Djokovic

The crowd's elation was quickly cut short when Federer rushed forward and an ice-cold Djokovic hammered a forehand into the net-cord. The deflection whistled past the Swiss's racquet.

(Federer's) loved. He's appreciated. He's respected around the world. For me it's normal in a way. I'm trying obviously to enjoy my time ... but also focus on the positive energy rather than negative, rather than getting frustrated for that.

Serbian tennis player Novak Djokovic

It gave the Serb his only break point of the set but he duly took it with a sumptuous cross-court return and stayed firm to serve out the set to love.

"That was a crucial break," said 28-year-old Djokovic.

"Obviously I didn't want to allow him to come back to the match and give him an opportunity maybe to take the match to the fifth."

Djokovic has won five titles at Melbourne Park but is unlikely to rely on much crowd support in the final.

Business-like to the end, Djokovic said there was no point worrying about it.

"For me it's normal in a way. I'm trying obviously to enjoy my time, to do the best that I can with the tennis racquet, but also focus on the positive energy rather than negative, rather than getting frustrated for that."